1. Field of the Invention
The present invention relates to an evaporated fuel processing apparatus adapted to collect evaporated fuel generated in a fuel tank into a canister and then purge the collected evaporated fuel into an intake passage of an engine and, more particularly, to an evaporated fuel processing apparatus provided for an engine with a supercharger.
2. Description of Related Art
Some conventional arts related to an evaporated fuel processing apparatus for an engine with a supercharger are disclosed in for example the following patent documents; Patent document 1 (Japanese patent unexamined publication No. Sho 62-18747, particularly, pages 1-2 and FIG. 2), Patent document 2 (Japanese patent publication No. Sho 59-563, particularly, pages 1-3 and FIG. 2), and Patent document 3 (Japanese patent publication No. Hei 5-10216, particularly, pages 2-7 and FIGS. 1 and 5).
Patent Document 1 discloses an apparatus constructed to purge evaporated fuel collected in a canister into an intake passage by utilizing purge passages configured in a double purging system in response to operation/nonoperation of a supercharger. During supercharging that the pressure in an intake passage positioned downstream of a throttle valve (a restriction valve) is a positive pressure, a change-over valve is opened to purge evaporated fuel from the canister into the intake passage located upstream of a supercharging impeller. The change-over valve is a diaphragm type valve which opens when senses pressure in the intake passage located downstream of the throttle valve during supercharging.
Patent document 2 discloses an apparatus using purge passages configured in a double purging system, as with the apparatus in the document 1. Specifically, This apparatus is provided with a first purge passage (a purge line) for purging evaporated fuel from a canister into an intake passage located downstream of a throttle valve (an intake air restriction valve) and a second purge passage for purging the evaporated fuel from the canister into an intake passage located upstream of a compressor in a turbocharger. In an operating condition of the turbocharger, the compressor feeds supercharged air into the canister to thereby force the evaporated fuel out of the canister into the purge passage, thus purging the evaporated fuel into the intake passage upstream of the compressor. The second purge passage is provided with no valve or the like to control the flow of evaporated fuel.
Patent document 3 discloses an apparatus using purge passages configured in a double purging system, as with the apparatus in the documents 1 and 2. This apparatus is constructed, differently from that in the document 2, to take in air for purging evaporated fuel from an intake passage positioned upstream of a compressor in a turbocharger through an intake air introducing passage and introduce the air into a canister. In this apparatus, the purge passage for purging evaporated fuel into the intake passage located upstream of the compressor is provided with no valve or the like to control the flow of evaporated fuel.
In the apparatus of the document 1, however, since the change-over valve is a diaphragm type valve, a response delay in opening and closing the change-over valve would become problems as below. For example, when an engine is in a decelerating condition, fuel cut is generally performed in the engine. However, there may be cases where a supercharger operates by inertia even just after deceleration, causing a delay in opening the change-over valve. Accordingly, the evaporated fuel is caused to flow in the intake passage upstream of the supercharging impeller. The evaporated fuel at this time would not burn or incompletely burn in a combustion chamber, which results in a deterioration in exhaust gas. To avoid such problems, it is conceivable to provide a check-over valve in the purge passage. Since a negative pressure produced in the intake passage upstream of the supercharging impeller is relatively small, the pressure to open the check valve has to be set at a relatively small pressure. Consequently, the check valve tends to close later during deceleration of the engine and the evaporated fuel also may be caused to flow in the intake passage.
In the above documents 2 and 3, any valve or the like is not provided in the purge passage connected in communication with the intake passage upstream of the compressor. Accordingly, when the supercharger operates by inertia just after deceleration of the engine, the evaporated fuel is also caused to flow in the intake passage, leading to a deterioration in exhaust gas. To avoid such problems, a check valve may be provided in the purge passage. However, it can be hardly said that there is no possibility of causing a delay in closing the check valve during deceleration of the engine. This also may cause the evaporated fuel to flow in the intake passage.